Last week The Mail on Sunday provoked an international storm by publishing a new official world temperature graph showing there has been no global warming since 1997.

The figures came from a database called Hadcrut 4 and were issued by the Met Office and the Climatic Research Unit (CRU) at East Anglia University.

We received hundreds of responses from readers, who were overwhelmingly critical of those climate change experts who believe that global warming is inevitable.

But the Met Office, whose lead was then followed by climate change campaigners, accused The Mail on Sunday of cherry-picking data in order to mislead readers. It even claimed it had not released a ‘report’, as we had stated, although it put out the figures from which we drew our graph ten days ago.

The Mail on Sunday revealed figures which appeared to show a 16-year 'pause' in global warming

Another critic said that climate expert Professor Judith Curry had protested at the way she was represented in our report. However, Professor Curry, a former US National Research Council Climate Research Committee member and the author of more than 190 peer-reviewed papers, responded: ‘A note to defenders of the idea that the planet has been warming for the past 16 years. Raise the level of your game. Nothing in the Met Office’s statement . . . effectively refutes Mr Rose’s argument that there has been no increase in the global average surface temperature for the past 16 years.

‘Use this as an opportunity to communicate honestly with the public about what we know and what we don’t know about climate change. Take a lesson from other scientists who acknowledge the “pause”.’

The Met Office now confirms on its climate blog that no significant warming has occurred recently: ‘We agree with Mr Rose that there has only been a very small amount of warming in the 21st Century.’

Here, we answer some of the key questions on climate change – and invite readers to make their own choice . . .

Q) Is the world warming or not?

A) The Hadcrut 4 figures that show a ‘pause’ in warming lasting nearly 16 years are drawn from more than 3,000 measuring stations on land and at sea. Hadcrut 4 is one of several similar global databases that reveal the same thing: that since January 1997 there has been no statistically significant warming of the Earth’s surface.

Between 1980 and the end of 1996, the planet warmed at a rate close to 0.2 degrees per decade. Since then, says the Met Office, the trend has been a much lower 0.03 degrees per decade.

However, world average temperature measurements are subject to an error of plus or minus 0.1 degrees, while any attempt to calculate a trend for the period 1997-2012 has an in-built statistical error of plus or minus 0.4 degrees. The claim that there has been any statistically significant warming for the past 16 years is therefore unsustainable.

Q) Why does it matter if the world is warming or not?

A) For years, the Government’s energy and climate policy has been dominated by the belief that we need swift, drastic and expensive reductions in carbon dioxide emissions to avert imminent catastrophe. In September, The Guardian claimed there were ‘less than 50 months to avoid climate disaster’.

These fears are based on computer models that show temperatures continuing to rise in step with levels of CO2.

The 2007 Fourth Assessment Report of the UN Inter-governmental Panel on Climate Change (IPCC) said: ‘For the next two decades, a warming of about 0.2 degrees Celsius per decade is projected for a range of emission scenarios’ – a prediction it said was solid because this rate of increase was already being observed.

But while CO2 levels have continued to rise since 1997, warming has paused. This leads Prof Curry to say the IPCC’s models are ‘incomplete’, because they do not adequately account for natural factors such as long-term ocean temperature cycles and a decline in solar output, which have suppressed the warming effects of CO2.

The Met Office and the CRU’s Professor Phil Jones say a ‘plateau’ of between 15 and 17 years is to be expected. But if the warming does not start again soon, the models will be open to challenge.

Q) Did The Mail on Sunday ‘cherry-pick’ data to disguise an underlying warming trend?

A) Some critics claim this newspaper misled readers by choosing start and end dates that hide the continued warming.

In fact, we looked at the period since 1997 because that’s when the previous warming trend stopped, and our graph ended in August 2012 because that is the last month for which Hadcrut 4 figures were available.

In April, the Met Office released figures up to the end of 2010 – an extremely warm year – which meant it was able to say there had been a statistically significant warming trend after 1997, albeit a very small one. However, 2011 and 2012 so far have been much cooler, meaning the trend has disappeared. This may explain why the updated figures were issued last week without a media fanfare.

Q) But isn’t it true that the science is ‘settled’?

A) Some scientists say the pause is illusory – if you strip out the effects of El Nino (when the South Pacific gets unpredictably warmer by several degrees), and La Nina (its cold counterpart), the underlying warming trend remains. Both phenomena have a huge impact on world weather.

Other experts point out one of the biggest natural factors behind the plateau is the fact that in 2008 the temperature cycle in the Pacific flipped from ‘warm mode’, in which it had been locked for the previous 40 years, to ‘cold mode’, meaning surface water temperatures fell. A cold Pacific cycle causes fewer and weaker El Ninos, and more, stronger La Ninas.

Prof Curry said that stripping out these phenomena made ‘no physical sense’. She added that natural phenomena and the CO2 greenhouse effect interact with each other, and cannot meaningfully be separated. It’s not just that the ‘cold mode’ has partly caused the plateau.

According to Prof Curry and others, the previous warm Pacific cycle and other natural factors, such as a high solar output, accounted for some of the warming seen before 1997 – some say at least half of it.

Other scientists say that heat has somehow been absorbed by the waters deep in the oceans. However, the evidence for this is contested, and there are no historical records with which to compare recent deepwater readings.

In the wake of the pause, the scientific ‘consensus’ looks much less settled than it did a few years ago.

Q) When will warming start again?

A) The truth is no one knows. It is likely that in the 2020s, the Atlantic cycle – currently in warm mode – will also flip to cold, so that for some years both the Pacific and Atlantic cycles will be cold at the same time. When this happens, world temperatures may decline, as they did in the Forties.

Prof Curry said: ‘If we are currently in a plateau and possibly headed for cooling, then sometime in the middle of the century we would likely see another period with a large warming trend.’
She added: ‘Because of natural variability, it is impossible to pinpoint what 2100 would look like. The climate sensitivity to greenhouse warming is still pretty uncertain, and it is not clear whether or to what extent man-made factors will dominate the climate of this period.’

For the world to be two degrees warmer in 2100 than it is now – as the IPCC has predicted – warming would not only have to restart but also proceed much faster than it has before.

Since 1880, temperatures have risen by around 0.75 degrees.

Q) But isn’t the world still much warmer than at any time in recorded history?

A) Ever since it was published on the cover of the IPCC’s Third Assessment report in 2001, the ‘hockey stick’ graph showing stable or declining temperatures since the year 1000, followed by a steep rise in the 20th Century, has been controversial. There were no thermometers in 1000, so scientists use ‘proxy’ data from items such as tree rings, lake sediments and ice cores.

The hockey stick authors have also been accused of eliminating the ‘medieval warm period’ (MWP) at the end of the first millennium.

Two new separate peer-reviewed studies, published in prestigious academic journals last week, reinstated it. The first study, led by Bo Christiansen of the Danish Meteorological Institute, concluded: ‘The level of warmth during the peak of the MWP in the second half of the 10th Century, equalled or slightly exceeded the mid-20th Century warming.’

There was also a pronounced warming period in Roman times.

Q) So where does that leave us?

A) Despite The Guardian’s bold claim that we have ‘50 months to save the world’, other evidence suggests that there are still decades left in which to plan an energy strategy driven by something other than panic.

In Britain, in the short to medium term, that would mean building modern ‘dual cycle’ gas power stations, which produce very clean energy and, unlike inefficient wind turbines, do not require subsidies to be economic.

In the longer term, we could be investing heavily in research into new forms of zero-carbon power, such as nuclear fusion, which are much closer to reality than most people realise.

Q) Surely we can leave it to our elected representatives to research all the arguments thoroughly and then act accordingly with our taxes?

A) Tim Yeo is the chairman of the Commons Select Committee on Energy and Climate Change, which advises the Government on energy policy. Lord Deben is chairman of the Government Climate Change Committee, which also gives direct advice on emissions targets.
Both Mr Yeo and Lord Deben have significant personal stakes in the ‘renewable’ energy industry, which benefits to the tune of billions of pounds a year from wind subsidies.